In the course of a lifetime, a significant number of persons will suffer serious physical injuries and medical incidents and conditions which may be survivable and allow a degree of recovery but, nevertheless, leave a more or less intractable degree of impairment of some capabilities. Some injuries to the head and physical incidents such as stroke which cause some loss of some brain and/or spinal cord function are particularly serious and often result in disabilities or physical impairments which compromise or even preclude some activities which are extremely important and substantially essential to what is considered to be a reasonably normal and independently functional life style in a community.
Stroke is one of the leading causes of disability in the United States with roughly 750,000 individuals being affected each year. The yearly cost of stroke is estimated at nearly 30 billion dollars in direct medical costs and nearly 20 billion dollars is lost productivity. Many people who survive stroke are left with severe and persistent disabilities. Among these persistent conditions is hemiparesis, a weakness on one side of the body, which can impair the ability to walk. While the majority of stroke survivors will regain some limited ability to walk, 40% will require assistance with walking and, of those who eventually become independent, 60% will still achieve only limited community ambulation. Fewer than 20% of stroke victims will achieve unlimited community ambulation.
In a recent study, over 90% of stroke victims considered the ability to walk sufficiently to participate in the community to be important and 40% considered that capability to be essential. Therefore restoration of a walking gait is a major goal of rehabilitation of victims of stroke and accidents having similar hemiparetic effects.
Walking or gait is a person's natural way of moving from one location to another and is the most efficient way for a person to travel short distances. In a normally functioning person, the lower limbs have the ability to adapt to different surfaces, ground topologies and obstacles such as uneven ground or stairs. Because of the importance of walking, patients will generally strive to retain or regain the ability to walk, notwithstanding severe impairment.
In early human development, many skills involving more or less repetitive movements of limbs or coordination among muscle groups, such as speech and ambulation which are necessary to functioning in a community, are learned to the point of being almost reflexive in nature. Many more involving movement and/or coordination such as riding a bicycle, skating, sports skills and performing on musical instruments can also be learned to a similar degree. Such learning is sometimes colloquially referred to as “muscle memory”. When a person having learned such skills suffers a stroke or injury causing hemiparesis, the muscles on one side of the body do not respond normally and impair the performance of such skills. Moreover, muscles on the impaired side of the body and the ability to control them may degenerate or atrophy from substantial disuse over a period of time and further impede recovery and the regaining of such skills.
It is well-established that repetitive movement against resistance can result in improved muscle tone and produce muscle growth as well as improve cardiovascular fitness even in persons of relatively advanced age. Movement against a weight is a classical form of such exercise. In recent years, many more or less sophisticated devices have been designed and built which not only provide such resistance in an easily controllable manner with reduced likelihood of injury but also allow some isolation of particular muscle groups during particular repetitive motions. Other types of exercise apparatus have also been developed to simulate some normal activities involving repetitive motion against resistance more or less closely. However, for normal persons, the degree of simulation of a normal activity is more important for the larger muscle groups to increase the exercise value of the repetitive motion against resistance than for the smaller muscle groups that would be important to the productive value of the activity that is being simulated. That is, some particulars of a complex repetitive motion being simulated may be altered in the interest of simplicity and/or robustness of the exercise apparatus or to place parts of the body at a relative mechanical disadvantage or to isolate particular muscle groups in order to maximize the exercise value of the motion but may be counterproductive in regard to the practice of activity, itself. In other words, use of exercise apparatus for development of the muscles involved in an activity does not necessarily improve the practice of the activity, itself, by the user of the exercise apparatus. Therefore, use of known commercially available exercise machines, while generally effective for obtaining maximal exercise value from their use, are of substantially reduced value in achieving rehabilitation of stroke or injury victims.